In constantly heated tubs with water circulation by a pump pathogenic germs, especially Legionellae, tend to multiply. To eliminate the danger of infection, chlorine or bromine compounds are added at regular intervals. There are also methods known which describe the injection of ozone into the water. All these methods are accompanied by odors. In addition there is a danger for the bath user in case the water treatment is not done regularly. Legionellae are also known to infect drinking water, where they can be combatted by addition of chlorine.